Smart interface technology

ABSTRACT

The present invention overcomes interface problems between proprietary handset ports on telephone base units and voice/data accessory products by allowing a user to automatically calibrate the telephone accessory product for an optimal interface match with the intended telephone base unit. This is accomplished through the use of a &#34;Smart Interface Technology&#34; (SIT) integrated chip set consisting of a full custom analog and semi-custom digital integrated circuit. The SIT incorporates three different methods for &#34;learning&#34; the characteristics of 4-wire port modular interfaces found in all telephone station sets. Basically, these methods determine the appropriate 4-wire terminal configurations, the transmit and receive channels of the intended telephone base unit, and adjust the channel sensitivities until an optimal and clear signal is provided for the user.

This is a division of U.S. patent application Ser. No. 08/625,398, filedMar. 27, 1996, the contents of which are hereby incorporated byreference.

FIELD OF THE INVENTION

This invention relates to the field of telephony. More particularly,this invention relates to a device capable of providing a 4-wireinterface to any telephone base unit's handset/headset port using 2-wireeach send and receive lines.

BACKGROUND OF THE INVENTION

For purposes of this discussion, a telephone network can be consideredas being divided into two parts. The first part comprises everythingfrom the telephone company leading up to and including the CentralOffice (CO) termination point in a subscriber's home or office. Thesecond part comprises everything from the Central Office terminationpoint and includes the individual telephone sets connected directly tothis termination point as well as proprietary systems (Key/PBX) andtheir respective proprietary telephone sets.

Everything within the first part is regulated by the FederalCommunications Commission (FCC) and therefore has a standard to whichtelephone set and system manufacturers must base their interfaceequipment. This includes all devices connecting directly to the CentralOffice telephone network, including telephone sets and telephonesystems. One problem that the telephony industry faces is that the otherparts of the telephone network are not regulated, including anythingrelated to the telephone sets which is not connected directly to thetelephone network, such as proprietary telephone sets and all hand sets.

Private phones generally include a telephone base unit and modularaccessories, such as a handset/headset. Accordingly, telephonemanufacturers can and do develop independent interface systems betweentheir telephone base units and accessories such as handsets/headsets.This often precludes the use of a different type of handset/headset witha particular base unit without manual reprogramming. The problem isespecially apparent when dealing with Key and Private Branch Exchange(PBX) system station sets which are entirely proprietary in nature. Manymanufacturers are providing accessories which are provided as originalequipment with the base unit. Many of these accessory products provideboth voice and data solutions not offered in the telephone station setssuch as headset, teleconferencing, facsimile and modem communicationalternatives.

What is needed is an invention that will allow a user to automaticallycalibrate a commercially available non-regulated voice/data product toallow an effective interface. This would solve any incompatibilityproblems and provide users with greater choices and flexibility whenselecting telephone equipment.

SUMMARY OF THE INVENTION

The present invention overcomes interface problems between proprietaryhandset ports on telephone base units and voice/data accessory productsby allowing a user to automatically calibrate the telephone accessoryproduct for an optimal interface match with the intended telephone baseunit. This is accomplished through the use of a "Smart InterfaceTechnology" (SIT) integrated chip set consisting of a full custom analogand semi-custom digital integrated circuit. The SIT incorporates threedifferent methods for "learning" the characteristics of 4-wire portmodular interfaces found in most telephone station sets. These methodsdetermine the appropriate 4-wire terminal configurations, the transmitand receive channels of the intended telephone base unit, and adjust thechannel sensitivities until an optimal and clear signal is provided forthe user.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a flow model of a "Central Office (CO) DialtoneLearning Sequence."

FIG. 2 illustrates a flow model of the "Automated 800 LearningSequence."

FIG. 3 illustrates a diagram of the SIT Data Transmission technique usedfor the "Automated 800" and "Manual 800" Learning Sequences of thepresent invention.

FIG. 4 illustrates switching algorithms for the system.

FIG. 5 is a continuation of the switching algorithms of FIG. 4.

FIG. 6 illustrates a block diagram of the regulated and non-regulatedportions of a typical telephone interface configuration as it relates toboth the Central Office and the "Smart Interface Technology" (SIT)system connection of the present invention.

FIG. 7 illustrates a block diagram of the SIT system including afull-custom analog and semi-custom digital microcontroller integratedcircuit.

FIG. 8 illustrates a block diagram of the SIT full-custom analogintegrated circuit of the present invention.

FIG. 9 illustrates a block diagram of 4×4 crosspoint switch and shuntresistor arrays.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 is a flow model of the "CO Dialtone Learning Sequence." This isthe primary method the SIT system uses to "learn" the characteristics ofthe telephone interface. The "CO Dialtone Learning Sequence" isautomatic and transparent to the end user.

Upon initial system power-up, such as the first time batteries areinstalled, a "CO Dialtone Search" routine is enabled to detect andlocate a CO dialtone signal on any combination of the 4-wire interfacelines from the telephone base unit. When the CO dialtone is detected,the "CO Dialtone Learning Sequence" will be fully enabled.

The "CO Dialtone Learning Sequence" is a one time activation process.After a successful "learn sequence" has been executed, the appropriatebit addressable latch 1 settings are stored from the digital MCU 100into the EEPROM 300, in order to maintain the correct settings in theevent of a power failure. Subsequent CO dialtones will not enable thelearning sequence unless a system reset is performed to re-enable thelearning routine. The "CO Dialtone Learning Sequence" is re-enabled by auser depressing the system reset switch 258 for a minimum of fiveseconds or by a soft system reset which is accessed remotely.

The "CO Dialtone Learning Sequence" starts with the location of the COdialtone. Location of the CO dialtone indicates the proper receivelines. The receive input step attenuator then adjusts the receivechannel sensitivity based on reference levels as described above. Thetransmit lines are then selected and the transmit output step attenuatoradjusts the transmit channel sensitivity based on reference levels.

FIG. 2 illustrates the flow models of the SIT "Automated 800 LearningSequence." Due to the lack of regulation as it relates to Key and PBXsystem station sets, there is a wide variation of sidetonecharacteristics which may be encountered. Consequently, it is possiblethat occasionally, the learning method employed by the "CO DialtoneMethod" may not provide optimal overall SIT system performance. The"Automated 800 Method" provides a very accurate means for the SIT systemto "learn" the characteristics of a 4-wire telephone port interface.

The "Automated 800 Learning Method" involves interaction between a"Host" system located at the termination of the accessed telephone lineand the "SIT" system located at the end user's location. The user placesa call to a designated telephone number and is greeted by an "automatedattendant" message. In the case of a voice application such as a headsetinterface, the message instructs the user to momentarily depress thesystem reset switch 258, place the "handset/headset" switch to the"headset" position and press a key on the telephone set keypad. Thekeystroke interrupts the "auto attendant" message and the "Host" sends apreamble to the "SIT" system. When the preamble is detected, the"Automated 800 Learning Method" is enabled.

The "Automated 800 Learning Method" interaction between the "Host" and"SIT" systems is shown in the flow model illustrated in FIG. 2 and the"FSK Data Transmission Diagram" is illustrated in FIG. 3. The "Host"sends a preamble, for a predetermined amount of time, to the "SIT"system to initiate the "Automated 800 Learning Sequence." The "Host"then sends a 1 KHz reference signal, for a predetermined amount of time,for setup/calibration of the "SIT" system which it compares to aninternal reference and uses to ensure proper setup/calibration of the"SIT" system transmit channel. When the incoming 1 KHz reference levelis satisfied, the "Host" sends a level confirmation signal to the "SIT"system and a final "handshake" is generated between the "Host" and "SIT"systems signifying completion of the "Automated 800 Learning Sequence."

The SIT "Automated 800 Learning Sequence" begins by searching for thepreamble sent by the Host. Once the preamble is located, the properreceive lines are located. The receive channel sensitivity is thenadjusted in comparison to a receive level reference. Upon locating theproper receive lines, the transmit lines are selected and theirsensitivity is adjusted in comparison to a transmit level referencesignal.

A third and final interface method is the "Manual 800 Method." Thismethod is used when either of the previously described learningsequences fail to provide optimal performance with a particulartelephone port interface. The "Manual 800 Method" provides the user withthe ability to interact with a trained telephony technician whom has theability to adjust virtually all of the SIT parameters remotely with theuse of a second "Host" system.

The SIT system "CO Dialtone" and "Automated 800 Learning" methods willselect the most common configurations which satisfy the system'sperformance criteria. Occasionally this may not be the optimal "lineconfiguration" selection for all interface environments. Since there areno regulatory requirements governing the specific characteristics for4-wire handset port interfaces, there is a range of differentconfigurations. It is not uncommon for an electronic telephone set tocontain a handset port interface that will operate with multiple"line-configuration" settings. All of the configurations will provideacceptable system performance, occasionally however, a particularconfiguration will be more susceptible to unwanted radio-frequencyinterference or electromagnetic interference. In these cases, alternatecombinations must be selected for optimal system performance.

Alternate combinations can be implemented by a user placing a call to atechnical support staff member (tech) at a designated telephone-number.After determining the problematic symptoms, the technician has theability to enable the "CO Dialtone Learning Sequence," the "Automated800 Learning Sequence" or the "Manual 800 Method" modes of operation bysending the appropriate sequence preamble. In the "Manual 800 Method"mode of operation, the technician can directly manipulate and change theparameters associated with the crosspoint switch array 2, the receiveinput step attenuator RX-2 or the transmit output step attenuator TX-S.

A block diagram of the regulated and non-regulated portions of a typicaltelephone interface configuration is illustrated in FIG. 6. Theconnection between the Central Office Lines of the telephone company 52and either a telephone set 54 or a telephone system 56 is regulated.Accordingly, telephone sets and systems from many manufacturers can allbe connected directly to the Central Office lines 52. The connectionbetween a telephone system 56 and a hybrid or digital telephone set 58is not regulated. The connection between a telephone set 54 or 58 and anaccessory 60 or 62 is also not regulated. Therefore, unless designed tointerface, one manufacturer's accessory may not operate with anothermanufacturer's telephone set.

The present invention provides a "Smart Interface Technology" (SIT)system interface 50 which provides an interface between accessories 60and 62 and telephone base units 54 and 58, having different protocols.The SIT system interface 50 allows a voice/data accessory 60 or 62 to beused with telephone base units 54 and 58 from multiple manufacturers,each having different protocols.

A block diagram of the SIT interface system of the present invention isillustrated in FIG. 7. The preferred embodiment of the SIT interfacesystem includes a full-custom SIT analog integrated circuit 200, asemi-custom digital microcontroller (MCU) 100, a 1-K serial EEPROM 300,a 4-wire telephone handset port 202 for coupling to a base unit, a voiceor data 2-channel interface input port 204 and output port 206.

The analog integrated circuit 200 is coupled to the telephone handsetport 202 through a 4-wire line interface. This interface allows for theestablishment and selection of the 2-wire each send (Tx) and receive(Rx) line pairs. As is well known, the send and receive pairs arefrequently not the same two lines in the port and may often share acommon return signal line.

Outputs P4 through P10 of the Digital MCU 100 are coupled to inputs LA0through LA4, DATA IN and MODE/ENABLE of the analog integrated circuit200, respectively. It is through this coupling that the digital MCU 100is able to control the various blocks within the analog integratedcircuit 200, which will be discussed below.

A receive signal Rx REF OUT of the analog integrated circuit 200 iscoupled to the analog/digital (A/D) input of the digital MCU 100 andprovides a sample of the input signal which the analog integratedcircuit 200 receives from the telephone base unit. The digital MCU 100uses this information to determine if the appropriate line configurationhas been selected and to control the receive and transmit channelsensitivities.

A signal TONE OUT from the digital MCU 100 is coupled to an input TXREFof the analog integrated circuit 200 and allows the digital MCU 100 toprovide a 1 KHz calibration transmit tone, through the analog integratedcircuit 200, to facilitate the appropriate selections of the transmitlines and transmit channel sensitivity setting.

An input RESET of both the Digital MCU 100 and analog integrated circuit200 is coupled to a power-on reset circuit and switch 250. The resetinput 250 allows the SIT system to be reset to activate one of the three"learning sequences" for the SIT system, of the present invention, to"learn" the characteristics of the telephone base unit. The resetcircuit 250 is coupled to a reset switch 258 which is activated by auser.

A serial 1K EEPROM 300 is coupled to the digital MCU 100 and stores the"learned" characteristics of the attached telephone base unit after asuccessful "learning sequence" has been executed. The "learned" settingsfor controlling the analog integrated circuit 200 are thereby maintainedwithin the EEPROM 300 in the event of a power failure.

A crystal oscillator 208 is coupled to inputs Xin and Xout of thedigital MCU 100 for generation of a clock signal by the digital MCU 100which controls the overall system timing of the SIT system interface 50of the present invention.

The receive volume control 252 is coupled to an input RX VC IN of theanalog integrated circuit 200 and is primarily used in voiceapplications whereby the user can adjust an output level of the receivedsignal to achieve a comfortable listening level.

The transmit volume control 254 is coupled to an input TX VC IN of theanalog integrated circuit 200 and is used as a fine tuning adjustmentfor precise level matching of the transmitted signal with the telephonebase unit.

The mute switch 256 is coupled to an input MUTE of the analog integratedcircuit 200 and is primarily used in voice applications whereby the usercan disable the transmit preamplifier to temporarily prevent any signalsfrom being transmitted to the telephone base unit.

The transmit channel voice or data input port 204 is coupled to an inputMIC IN on the analog integrated circuit 200. This is the primary inputpoint between the user and the SIT system of the present invention. Invoice applications, the input MIC IN is preferably coupled to anelectret type microphone.

The receive channel voice or data output port 206 is capacitivelycoupled from an output RX OUT of the analog integrated circuit 200 andprovides the equalized incoming signal from the telephone base unit tothe user. In voice applications, the output RX OUT is preferably coupledto an audio loudspeaker. The output RX OUT is also coupled to an inputALC IN of the analog integrated circuit 200 which acts as a compressorfor large unwanted signals which are potentially harmful to the user orinterface apparatus.

The digital MCU 100, analog integrated circuit 200 and serial 1K EEPROM300 are preferably battery powered and can operate over a supply rangeof 3 to 5 volts DC. The digital MCU 100 is coupled to the bandgap DCreference voltage generated by the analog integrated circuit 200.

Timing capacitors 210, 212, 214 and 216 are coupled to inputs XPND1,XPND2, ALC TC2 and ALC TC1, of the analog integrated circuit 200,respectively. These timing capacitors 210, 212, 214 and 216 are thencoupled to various blocks within the analog integrated circuit 200 andused to control the various attack and release times associated withexpander, compressor and sleep circuits.

Filter capacitors 218, 220, 222 and 224 are coupled to inputs TX FILT1,TX FILT2, RX FILT1 and RX FILT2 of the analog integrated circuit 200,respectively. These filter capacitors 218, 220, 222 and 224 are thencoupled to the receive and transmit channel output amplifiers and areused to set the channel frequency response characteristics.

Coupling capacitor 226 is coupled between a receive input RX1 IN and areceive output RX1 OUT of the analog integrated circuit 200. Couplingcapacitor 228 is coupled between a receive input RX2 IN and a receiveoutput RX2 OUT of the analog integrated circuit 200. Coupling capacitor230 is coupled between a transmit input TX1 IN and a transmit output TXOUT of the analog integrated circuit 200. Coupling capacitor 232 iscoupled between an input TX2 RET of the analog integrated circuit 200and ground. Coupling capacitor 234 is coupled between the input MIC INof the analog integrated circuit 200 and the voice/data input port 204.Coupling capacitor 236 is coupled between an output RX OUT of the analogintegrated circuit 200 and the voice/data output port 206. The couplingcapacitors 226, 228, 230, 232, 234 and 236 are used to remove DC offsetand couple the AC input and output signals into and out of the varioussend and receive signal blocks found in both the receive and transmitchannels of the analog integrated circuit 200.

A system block diagram of the preferred embodiment of the SIT analogintegrated circuit 200 is illustrated in FIG. 8. The SIT analogintegrated circuit 200 is a full custom circuit that is designed tointerface directly to the telephone base unit and is controlled by thesemi-custom digital MCU 100, as illustrated in FIG. 7.

Within the analog integrated circuit 200, a 32 bit addressable latch 1includes inputs BA0-BA4 which are coupled to the pins LA0-LA4 of theanalog integrated circuit 200. An input DATA IN and output DATA OUT ofthe 32 bit addressable latch 1 are coupled to the pins DATA IN and DATAOUT, respectively, of the analog integrated circuit 200. An enable inputENABLE of the latch 1 is coupled to a mode latch 4 and to the pin ENABLEof the circuit 200. A reset input RESET of the latch 1 is coupled to themode latch 4 and to the pin RESET of the circuit 200. The mode latch 4is controlled by the signals from the pins ENABLE and RESET and saves acurrent mode which the circuit 200 is operating in. Outputs b0-b15 ofthe latch 1 are coupled to control a 4×4 crosspoint switch array 2.Outputs b16-b18 of the latch 1 are coupled to control a receive inputmultiplexer 5. Outputs b19-b21 of the latch 1 are coupled to control atransmit output multiplexer 6. Output b22 of the latch 1 provides areceive/transmit disable/enable control signal. Output b23 of the latch1 is coupled to an input ON of a switchable dialtone filter RX-6. Outputb24 of the latch 1 is coupled to an input PR of a flip-flop 7, to aninput A of a multiplexer 9 and to a clock input CLK of the switchabledialtone filter RX-6. Output b25 of the latch 1 provides a signal S/HSPEED which is coupled to an input C of a flip-flop 7 and to a selectinput of the multiplexer 9. Outputs b26-b31 of the latch 1 are coupledto control a 100 ohm shunt select array 3.

The four lines of the 4-wire phone port 202 are coupled as inputs to thearray 3. The array 3 is also coupled to the array 2. Outputs of thearray 2 are coupled to the pins RX1 OUT and RX2 OUT of the analogintegrated circuit 200 to provide an output received signal. Inputs ofthe array 2 are coupled to the pins TX1 IN and TX2 RTN of the circuit200, to receive a transmit signal. Outputs of the multiplexer 5 arecoupled as inputs D0, D1 and D2 of a receive input step attenuator RX-2.Two sets of control inputs MRX-1, 2, 3, and BITS 16, 17, 18 are coupledto multiplexer 5. Outputs of multiplexer 6 are coupled as inputs D0, D1and D2 of a transmit output step attenuator TX-5. Two sets of controlinputs MTX-1, 2, 3 and BITS 19, 20, 21 are coupled to multiplexer 6. Anoutput MODE of the mode latch 4 is coupled to the selection controlinputs of multiplexers 5 and 6.

The receive input pins RX1 IN and RX2 IN of the analog integratedcircuit 200 are coupled as inputs to a receive input differentialamplifier RX-1. An output of the amplifier RX-1 is coupled as an inputto the receive input step attenuator RX-2. An output of the attenuatorRX-2 is coupled as an input to a receive voltage controlled amplifier(VCA) RX-3, as an input to a switchable dialtone filter RX-6 and to apin TEST RX LEV of the circuit 200 for testing the level of the receivedsignal output from the attenuator RX-2.

A receive voltage control pin RX VC IN of the circuit 200 is coupled asa control input to the receive VCA RX-3. Automatic level control (ALC)pins ALC TC1, ALC TC2 and ALC INPUT of the circuit 200 are coupled asinputs to an ALC circuit RX-5. An output of the ALC circuit RX-5 iscoupled as an ALC input to the receive VCA RX-3. An input of the receiveVCA RX-3 is coupled to a receive filter pin RX FILT1 of the circuit 200and as an input to a receive output amplifier RX-4. An output b22 of thelatch 1 is coupled as a receive disable input to the amplifier RX-4. Anoutput of the amplifier RX-4 is coupled to a receive filter pin RX FILT2of the circuit 200. A receive output signal is provided as an outputfrom the amplifier RX-4 and coupled to a receive output pin RX OUT ofthe circuit 200.

A transmit reference input pin TX REF INPUT of the circuit 200 iscoupled as an input to a transmit reference filter TX-1. An output b24of the latch 1 is coupled as a clock input to the filter TX-1. Atransmit input pin TX INPUT of the circuit 200 is coupled as an input toa transmit pre-amplifier circuit TX-2. A mute pin MUTE of the circuit200 is coupled as an input to the pre-amplifier circuit TX-2. The outputb22 of the latch 1 is coupled as transmit enable input to thepre-amplifier circuit TX-2. An output of the pre-amplifier circuit TX-2is coupled to an output of the filter TX-1 and as an input to a transmitVCA TX-3 and an expander circuit TX-4.

Pins XPDI CAP and XPD2 CAP of the circuit 200 are coupled as inputs tothe expander circuit TX-4. An output of the expander circuit TX-4 iscoupled as an input to the transmit VCA TX-3. A transmit pin TX VCIN ofthe circuit 200 is coupled to an input of the transmit VCA TX-3. Anoutput of the transmit VCA TX-3 is coupled as an input to the transmitoutput step attenuator TX-5. An output of the attenuator TX-S is coupledas an input to a transmit output amplifier TX-6. Transmit filter pins TXFILT1 and TX FILT2 of the circuit 200 are coupled to inputs of theamplifier TX-6. A transmit output signal is output from the amplifierTX-6 and coupled to the transmit output pin TX OUT of the circuit 200.

An input D of the flip-flop 7 is coupled- to ground. An output Q of theflip-flop 7 is coupled as a reset input to a 1/2 dividing circuit 8 anda 1/16 dividing circuit 10. An output of the 1/2 dividing circuit 8 iscoupled as an input B to the multiplexer 9. An output O of themultiplexer 9 is coupled as an input to the 1/16 dividing circuit 10 andto an anti-alias filter circuit RX-7. An output of the switchabledialtone filter circuit RX-6 is coupled as an input to the filter RX-7.An output of the filter RX-7 is coupled as an input to a sample and holdcircuit RX-8. An output of the 1/16 dividing circuit 10 is coupled as aninput to the sample and hold circuit RX-8. An output of the sample andhold circuit RX-8 is coupled to a receive level reference pin RX LEVELREF of the circuit 200.

A timing capacitor pin TIME CAP of the circuit 200 is coupled as aninput to a sleep circuit and system power supply 11. Power supply inputpins VCC, RXVss, TXVss and DIGVss of the circuit 200 are coupled asinputs to the sleep circuit and system power supply 11. The inputs RX1and RX2 to the amplifier RX-1 are coupled as inputs to the sleep circuitand system power supply 11. An output of the sleep circuit and systempower supply 11 is coupled to a bandgap reference circuit 12. An outputof the bandgap reference circuit 12 is coupled to a voltage referencepin VREF of the circuit 200.

The digital MCU 100 is able to address and manipulate the 32 bitaddressable latch 1, thereby controlling the 4×4 crosspoint switch array2 and 100 ohm resistor shunt array 3, within the analog integratedcircuit 200. The crosspoint switch array 2 has four input ports whichare directly coupled to a four line telephone base unit jack 202 throughthe array 3, as illustrated by the lines 1-4. The 100 ohm resistor shuntarray 3 contains six switchable shunt resistors, is configured inparallel with the crosspoint switch array 2 input ports, and is capableof providing a 100 ohm shunt resistance between any of the 4 lineinputs.

When a telephone accessory including the interface system of the presentinvention is first plugged into a telephone base unit, the accessory maynot operate because it has not yet been optimally configured toelectronically communicate with the telephone base unit. A CentralOffice dialtone is applied by the telephone base unit to two of thelines of the jack 202. Under control of the digital MCU 100, theaddressable latch 1 manipulates the crosspoint array 2 and the shuntselect array 3 by sequentially coupling pairs of line input ports untila CO dialtone is sensed by the digital MCU 100 in the receive channel.This information is then latched for further analysis by the digital MCU100.

The two receive lines through which a CO dialtone is detected, arecoupled to the receive input differential amplifier RX-1 which isterminated with a known resistive impedance. In the preferredembodiment, the resistive impedance is 1K ohm.

A 28 dB energy variance exists between telephones that are commerciallyavailable. Accordingly, in a voice application, a telephone headset orother accessory that is configured to work with one telephone base unitcould provide an uncomfortably loud signal when used with a second baseunit or be significantly quiet when used with a third telephone baseunit. To solve this problem, the output of the differential amplifierRX-1 is coupled to the input of the receive step attenuator RX-2. Thereceive step attenuator RX-2 is initially configured to provide maximumattenuation and then increases the receive signal in 4 dB incrementsuntil a predetermined target reference level is sensed by the digitalMCU 100, thereby equalizing the receive channel sensitivity. The receivestep attenuator RX-2 is coupled to the receive input multiplexer 5 whichis controlled by the 32 bit addressable latch 1. The digital MCU 100controls both the bit addressable latch 1 and the receive inputmultiplexer 5 thereby setting the attenuation by the step attenuatorRX-2.

The equalized receive signal is then coupled to the voltage controlledamplifier RX-3 which can have fixed gain or allow the user to manuallycontrol the volume level of the receive signal through a port RX VC INwhich is coupled to the voltage controlled amplifier RX-3. An output ofthe automatic level control circuit RX-5 is also coupled to an ALCcontrol input on the voltage controlled amplifier RX-3 and is capable ofcontrolling the amplifier gain.

The automatic level control circuit RX-5 acts as a dynamic outputlimiting system with an overall dynamic range of 40 dB. The automaticlevel control circuit RX-5 input samples the output level of the receivechannel and has a selectable limiting threshold as shown in FIG. 7 whichis adjusted using the ALC level adjust circuit 260. The automatic levelcontrol circuit RX-5 is capable of limiting the output level of thereceive signal to a predetermined level to prevent large unwanted andpotentially harmful signals from reaching a user. In voice applications,the user's ears will be protected from prolonged high decibel sounds bythe automatic level control circuit RX-5, thereby preventing potentialdamage to the user's hearing. The ALC timing capacitors 214 and 216,illustrated in FIG. 7, are coupled to the pins ALC TC1 and ALC TC2 andare used to set the attack and release timing characteristics of the ALCcircuit RX-5.

The equalized receive signal is output from the receive VCA RX-3 andcoupled as an input to the receive output amplifier RX-4 which iscapable of driving resistive, capacitive and inductive loads via thereceive output port RX OUT for compatibility with voice or datainterfaces. The filtering capacitors 222 and 224, illustrated in FIG. 6,and coupled to the pins RX FILT1 and RX FILT2 of the circuit 200 areused to determine the receive channel frequency response.

The digital MCU 100 monitors the receive signal by sampling the signalthrough the receive level reference port RX LEVEL REF. The receivesignal sample for the digital MCU 100 is taken at the output of thereceive step attenuator RX-2 and is filtered by the dialtone filterRX-6, then the anti-alias filter RX-7. The receive signal sample isfinally coupled into the sample and hold circuit RX-8 prior to beingpassed on to the receive level reference port RX LEVEL REF. The receivelevel reference port RX LEVEL REF is coupled directly to the A/D inputof the digital MCU 100. The digital MCU 100 controls the dialtone filterRX-6, anti-alias filter RX-7 and sample and hold circuit RX-8 via the 32bit addressable latch 1 and synchronizes these switched capacitorfilters with the use of the clock circuitry shown in the blocks 7, 8, 9and 10.

Once the receive lines are determined and the channel sensitivity isadjusted for optimal performance, the transmit lines and sensitivity arethen determined. Based on the selected receive lines, certain transmitline configurations are highly probable and are prioritized in thesystem algorithms.

Utilizing the sidetone characteristics of telephone base units, thedigital MCU 100 will continue to monitor the receive signal path via thereceive level reference output port RX LEVEL REF for calibration of thetransmit channel.

A transmit preamplifier TX-2 is used as the interface for the user voiceor data input signal and provides some preamplification of the inputsignal in addition to a channel mute user portion. It should be notedthat this mute stage is disabled during the "leaming" process to preventthe user from inserting a variant signal into the transmit path. Theoutput of the transmit preamplifier TX-2 is coupled to the transmit VCATX-3 and the transmit expander circuit TX-4.

During a "learning" procedure, the digital MCU 100 generates a 1 KHztransmit calibration signal into the transmit reference input port TXREF INPUT. The 1 KHz calibration signal is then coupled into thetransmit reference low pass filter TX-1 which is controlled by the 32bit addressable latch 1 and hence the digital MCU 100. The transmitreference low pass filter TX-1 filters out the odd harmonics of thecalibration signal and outputs the result to the transmit VCA TX-3 andthe expander circuit TX-4.

The input of the expander circuit TX-4 is coupled to the output of thetransmit preamplifier TX-2 and the transmit reference low pass filterTX-1. The expander circuit TX-4 differentiates input noise from thedesired signal. The expander circuit TX-4 output is coupled to a controlinput of the transmit VCA TX-3 and provides electronic noise reductionby attenuating the transmit VCA gain as it relates to unwantedbackground noise. The timing capacitors 210 and 212, illustrated in FIG.7 and coupled to the pins XPD1 and XPD2 are used to determine theexpander attack and release characteristics.

The transmit VCA TX-3 receives its input from the transmit preamplifierTX-2 and transmit reference low pass filter TX-1 and serves two primarypurposes. The transmit VCA TX-3 works in conjunction with the transmitexpander circuit TX-4 to provide electronic noise reduction and providesan overall transmit channel output level adjustment to allow preciseinterface matching via an optional transmit volume control function. Thetransmit volume control circuit 254 is illustrated in FIG. 7. The outputof the transmit VCA TX-3 is coupled to the transmit output stepattenuator TX-5.

The digital MCU 100 will begin manipulating the crosspoint switch array2 by sequentially coupling pairs of the transmit output ports startingwith the most probable pairs defined in the system algorithms. Adescription, which illustrates the system's switching algorithms, isshown in detail in FIGS. 4 and 5. The 1 KHz transmit calibration signalis therefore applied to the telephone base unit via the jack lines 202until the 1 KHz signal is sensed by the digital MCU 100 at the receivelevel reference output RX LEVEL REF. When the digital MCU 100 senses the1 KHz signal it will have successfully located the appropriate transmitlines and will latch the information and begin the transmit output stepattenuator TX-5 adjustment.

A 49 dB variance in transmit line sensitivity exists between telephonebase units that are commercially available. A precise sensitivityinterface match is critical for optimal performance of the transmittedsignal with the various telephone base units. To solve this problem, thesignal output of the transmit VCA TX-3 is coupled into the transmitoutput step attenuator TX-5 which effects the transmit output level. Thetransmit output step attenuator TX-5 is coupled to the transmit outputmultiplexer 6 which is controlled by the 32 bit addressable latch 1 andtherefore the digital MCU 100. The digital MCU 100 will adjust thetransmit step attenuator in 7 dB increments until a predetermined 1 KHztarget reference level is sensed by the digital MCU 100, therebyequalizing the transmit channel sensitivity to the appropriate level.The signal output of the transmit output step attenuator TX-5 is coupledto the transmit output amplifier TX-6.

The transmit output amplifier TX-6 is capable of providing a voltage orcurrent drive output and driving resistive, capacitive or inductiveloads. A coupling capacitor 230 is used to couple the transmit outputsignal from the pin TX OUT into the crosspoint switch array 2 throughthe transmit input pin TX1 IN. The filtering capacitors 218 and 220,illustrated in FIG. 7 and coupled to the pins TX FILT1 and TX FILT2 areused to determine the transmit channel frequency response.

To conserve on battery life of the power supply 11, the analogintegrated circuit 200 includes the sleep circuit within the powersupply 11. The sleep circuit 11 is coupled between the VCC port and themain IC block power supplies. The sleep circuit control input is coupledto the inputs RX1 and RX2 of the receive differential amplifier RX-1. Ifthe incoming broadband noise on the receive lines drops below a certainlevel, preferably -65 dBV, the sleep circuit begins a timing sequence asdetermined by the value of the sleep timing capacitor 218. If thebroadband receive signal does not exceed the -65 dBV threshold withinthe programmed timeframe, the analog integrated circuit 200 enters intothe sleep mode and shuts down. When the broadband receive signal exceedsthe -65 dBV threshold, the sleep timing sequence resets and the analogintegrated circuit "wakes up" within 5 milliseconds (ms).

The preferred embodiment for the analog integrated circuit 200 ispowered by any convenient power source which can be directly connectedto the pin VCC to serve as the primary circuit power supply. The bandgapreference circuit 12 develops a stable reference voltage for useinternally in the analog integrated circuit 200 and externally for thedigital MCU 100 and VCA control voltages.

A block diagram of the 4×4 crosspoint switch array 2 and the 100 ohmshunt resistor array 3 is illustrated in FIG. 9. The crosspoint switcharray consists of a 4×4 matrix of analog switches designed to connectlines 1-4 of the 4-wire phone port 202 to the two transmit and tworeceive channels in any order and polarity. It is under the control ofthe digital MCU 100, through the bit addressable latch 1, that theappropriate transmit and receive lines are determined, as describedabove.

The present invention has been described in terms of specificembodiments incorporating details to facilitate the understanding of theprinciples of construction and operation of the invention. Suchreference herein to specific embodiments and details thereof is notintended to limit the scope of the claims appended hereto. It will beapparent to those skilled in the art that modifications may be made inthe embodiment chosen for illustration without departing from the spiritand scope of the invention. Specifically, it will be apparent to one ofordinary skill in the art that the method of the present invention couldbe implemented in several different ways and the apparatus disclosedabove is only illustrative of the preferred embodiment of the presentinvention and is in no way a limitation.

We claim:
 1. A CO Dialtone Learning Sequence method of learning thecharacteristics of a telephone set with a 4-wire port interface whichcomprises the steps of:a. searching the 4-wire port interface of thetelephone set for a CO dialtone; b. detecting a CO dialtone; c.selecting receive lines; d. setting the receive channel sensitivity bycomparison with receive level references; e. selecting transmit lines;and f. setting the transmit channel sensitivity by comparison with atransmit reference signal.
 2. A Host Automated 800 Learning Sequencemethod of learning the characteristics of a telephone set with a 4-wireport interface which comprises the steps of:a. searching the 4-wire portinterface of the telephone set for a DTMF tone sent by a remote host; b.sending a preamble to a user; c. disabling a reference signal; d.enabling a level detect system; e. measuring an incoming transmitsignal; f. comparing the transmit signal against a transmit levelreference; g. sending a level confirmation signal.
 3. A SIT Automated800 Learning Sequence method of learning the characteristics of atelephone set with a 4-wire port interface which comprises the stepsof:a. searching the 4-wire port interface of the telephone set for apreamble; b. detecting the preamble; c. selecting receive lines; d.setting the receive lines' channel sensitivity by comparison with areceive level reference; e. selecting transmit lines; and f. setting thetransmit lines' channel sensitivity by comparison with a transmitreference signal.
 4. A Manual 800 method of learning the characteristicsof any telephone with a 4-wire port interface which comprises the stepsof:a. enabling a Manual 800 mode; b. sending a preamble to the telephoneset from a remote host wherein a human operator is positioned at alocation of the remote host; c. adjusting sensitivity of a transmitchannel under control of the human operator; d. adjusting sensitivity ofa receive channel under control of the human operator; and e. disablingthe Manual 800 mode.
 5. A central office dialtone method of configuringa telecommunications interface system having a signal processing circuithaving a receive signal path and a transmit signal path to appropriatelyinterface a telephone accessory with a handset port of a telephone baseunit having a plurality of electrical contacts, whereby the interfacesystem is configured for appropriately coupling the output contacts tothe receive signal path and the input contacts to the transmit signalpath including two electrical output contacts and two electrical inputcontacts, the method comprising steps of:a. searching the plurality ofelectrical contacts of the handset port of the telephone base unit for acentral office dialtone; b. detecting the central office dialtone acrossthe input electrical contacts; c. electrically coupling the inputelectrical contacts to the receive signal path; d. adjusting sensitivityof the receive signal path by comparing a level of the central officedialtone with a receive level reference; and e. electrically couplingthe output electrical contacts to the transmit signal path.
 6. Themethod according to claim 5 further comprising a step of adjustingsensitivity of the transmit signal path by applying a transmit referencesignal to the transmit signal path and monitoring receive signal pathwhich receives the transmit reference signal via a sidetonecharacteristic of the telephone base unit.
 7. The method according toclaim 5 wherein the step of electrically coupling the input electricalcontacts to the receive signal path includes a step of appropriatelyconfiguring a switch matrix.
 8. A remote host automated method ofconfiguring a telecommunications interface system having a signalprocessing circuit having a receive signal path and a transmit signalpath to appropriately interface a telephone accessory with a handsetport of a telephone base unit having a plurality of electrical contacts,whereby the interface system is configured for appropriately couplingthe output contacts to the receive signal path and the input contacts tothe transmit signal path including two electrical output contacts andtwo electrical input contacts, the method comprising steps of:a. forminga telephone connection between a remote host and the telephone baseunit; b. searching the plurality of electrical contacts of the handsetport of the telephone base unit for a signal sent by the remote host; c.detecting the signal sent by the host across the input electricalcontacts; d. electrically coupling the input electrical contacts to thereceive signal path; e. adjusting sensitivity of the receive signal pathby comparing a level of the signal sent by the host present in thereceive signal path to a receive level reference; f. disabling thesignal sent by the host; and g. electrically coupling the outputelectrical contacts to the transmit signal path.
 9. The method accordingto claim 8 further comprising a step of adjusting sensitivity of thetransmit signal path by applying a transmit reference signal to thetransmit signal path and monitoring receive signal path which receivesthe transmit reference signal via a sidetone characteristic of thetelephone base unit.
 10. The method according to claim 8 wherein thestep of electrically coupling the input electrical contacts to thereceive signal path includes a step of appropriately configuring aswitch matrix.
 11. A manual method of configuring a telecommunicationsinterface system having a signal processing circuit having a receivesignal path and a transmit signal path to appropriately interface atelephone accessory with a handset port of a telephone base unit havinga plurality of electrical contacts, whereby the interface system isconfigured for appropriately coupling the output contacts to the receivesignal path and the input contacts to the transmit signal path includingtwo electrical output contacts and two electrical input contacts, themethod comprising steps of:a. forming a telephone connection between aremote host and the telephone base unit wherein a human operator ispositioned at a location of the remote host; b. electrically couplingthe input electrical contacts to the receive signal path under controlof the human operator; c. adjusting sensitivity of the receive signalpath under control of the human operator; d. electrically coupling theoutput electrical contacts to the transmit signal path under control ofthe human operator; and e. adjusting sensitivity of the transmit channelsensitivity under control of the human operator.
 12. The methodaccording to claim 4 further comprising a step of enabling switchingalgorithms.